1. Field of the Invention
This invention relates to the formation of a layer of metal on a substrate and, in particular, to the formation of an anti-reflective coating (ARC) and/or ARC-containing layer that has a reduced roughness. More particularly, the present invention relates to the formation of a titanium- and/or tungsten-containing ARC layer on an aluminum- or aluminum alloy-containing metallization layer in an integrated circuit.
2. Description of the Related Art
Some metal deposition processes result in formation of grain boundaries in the deposited metal layer. Such grain boundaries may give rise to localized sites of high reactivity in the metal layer.
In particular, in integrated circuit fabrication, aluminum tends to be somewhat reactive with subsequently deposited titanium-tungsten alloy, particularly when the substrate is at a relatively high temperature (e.g., 480.degree. C.). This often results in localized formation of a TiWAl phase at the aluminum grain boundaries, causing formation of TiWAl "bumps" on the surface of the deposited aluminum layer. FIG. 1 is a cross-sectional representation of one such TiWAI "bump" at a grain boundary, as formed using a conventional process. As shown therein, numeral 110 references a grain boundary of a metallization layer 105, such as aluminum. As the ARC layer, such as TiW, is conventionally formed at high temperatures, deposition of a TiW layer 130 on the metallization layer 105 causes an underlying intermetallic phase 120 of TiWAl to be formed. Such an intermetallic phase 120 of TiWAl tends to form one or more "bumps" 140 above the reactive grain boundary. Because of these "bumps" 140 of intermetallic phase TiWAl 120, the overlying ARC layer 130 of TiW exhibits one or more corresponding "bumps" 150. These "bumps" 150 increase the surface roughness of the aluminum layer 105, causing problems during subsequent photolithography and metal etching processes. In the worst case, the "bumps" 140, 150 may be sufficiently large to adversely affect the yield of the metallization process and/or of the entire integrated circuit fabrication process.
It is, therefore, desirable to provide a method of forming an anti-reflective coating (ARC) and/or ARC-containing metal layer on a substrate that reduces the roughness of the coating or layer. More particularly, it is desirable to provide a method of forming a titanium- and/or tungsten-containing ARC layer on an aluminum- or aluminum alloy-containing metal layer in an integrated circuit, where the ARC layer may have a relatively uniform thickness and/or where the metal layer containing the ARC layer has a reduced roughness relative to similar metal layers formed by conventional processes.